Cleanup remaining class/struct fwd declarations

ipc/ipc_channel_nacl.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IPC_IPC_CHANNEL_NACL_H_
 #define IPC_IPC_CHANNEL_NACL_H_
 
 #include <deque>
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "base/memory/linked_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/process/process.h"
 #include "base/threading/simple_thread.h"
 #include "ipc/ipc_channel.h"
 #include "ipc/ipc_channel_reader.h"
 
 namespace IPC {
 
+class MessageAttachment;
+
 // Contains the results from one call to imc_recvmsg (data and file
 // descriptors).
 struct MessageContents;
 
 // Similar to the ChannelPosix but for Native Client code.
 // This is somewhat different because sendmsg/recvmsg here do not follow POSIX
 // semantics. Instead, they are implemented by a custom embedding of
 // NaClDescCustom. See NaClIPCAdapter for the trusted-side implementation.
 //
 // We don't need to worry about complicated set up and READWRITE mode for
@@ skipping 72 matching lines @@
   std::deque<linked_ptr<Message> > output_queue_;
 
   base::WeakPtrFactory<ChannelNacl> weak_ptr_factory_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(ChannelNacl);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_CHANNEL_NACL_H_